Write protection schemes to protect the data or information stored in a magnetic media such as a floppy disk has been accomplished heretofore through a "switch" on the media. When the media is placed into a reader, such as a floppy disk drive, the system will check if the "switch" is on or off to determine the protection status of the media. The "switch" is not an electrical switch but is merely an indicator. The position of the indicator reflects the status of the "switch" to the reader. Thus, for example, the reader can employ a light emitting source and sensor to detect the position of the indicator, and hence the status of the switch.
With such a protection scheme, a number of errors can arise. First, the software running on the computer which is connected to the reader may ignore the status of the switch and write to the media in any event and destroy the original contents. Secondly, the light emitting source and sensor within the reader may not function properly to either detect the status or to pass that information which is detected to the computer to which it is connected.
Similar to a magnetic storage media, semiconductor storage media, typically known as memory cards, have been proposed to store data or information. Typically, the semiconductor memory is in the form of electrically alterable non-volatile memory such as EEPROM. A memory card typically comprises a plurality of integrated circuit modules each containing an EEPROM memory array. In the context of being analogous to a magnetic storage media having its "switch" on the media, the memory card also uses a "switch" on the memory card to indicate the write protection status of the memory card.
In one prior art proposal, a Software Data Protection (SDP) scheme envisions a write protection circuit which is integrated with the memory array circuit on a single integrated circuit module. The write protection circuit employs a non-volatile register to store the writability status of the memory array circuit with which the write protection circuit is associated. The contents of the non-volatile register can only be written or rewritten by a special sequence of access codes. Since the non-volatile register is "on board" with the memory array circuit with which it is associated, the write protection scheme is "hard wired" with the memory array and may not be tampered with by the software nor is it subject to error by the hardware. Thus, the advantages of such a scheme is that the protection does not depend on external software or hardware and the protection setting is non-volatile. However, the SDP method is effective for only a single memory module at a time. Thus, for a memory card having a plurality of memory modules, the SDP scheme cannot be used effectively.